57 



pH value as a result of liming- is less than that shown in the 

 laboratory, owing in part to the reduction of the acidity of the 

 subsoil. Application of amounts of lime equivalent to the 

 Hutchinson-MacLennan " lime requirement " reduced the acidity 

 by an amount equal to +0.5 to +0.7 in pH value, but the soils 

 still remained appreciably acid. 



XXIX. E. M. Crowther. " Studies in Soil Reaction. 

 V. The Depth-distribution of Reaction and Floc- 

 culation in Continuously Manured Soils.'* Journal of 

 Agricultural Science, 1925. Vol. XV., pp. 232-236. 



The reactions of the unmanured and the limed and unlimed 

 portions of the sulphate of ammonia plots on Rothamsted Park 

 Grass and Woburn Barley plots change steadily with increasing 

 depth, and at 36in. still show the same relations as in the surface 

 soil. The difference in pH values between the limed and unlimed 

 portions is substantially constant at all depths down to 36in. 

 The reaction of the subsoil plays an important part in determining 

 the effect of liming. The subsoils from the sulphate of ammonia 

 plots at both centres are highly flocculated. Mixtures of 1 part 

 of soil with 5 parts of water exhibit complete llocculation in the 

 case of all samples below 9in. and the velocity of sedimentation 

 decreases and the volume of the final sediment increases regularly 

 and markedly with the depth. Such changes in soil texture pos- 

 sibly constitute an important factor in the effects due to a high 

 surface acidity. 



XXX. E. M. Crowther and W. S. Martin. " Studies in 

 Soil Reaction. VI. The Interaction of Acid Soils, 

 Calcium Carbonate and Water, in Relation to the 

 Determination of 'Lime Requirements.' " Journal of 

 Agricultural Science, 1925. Vol. XV., pp. 237-255. 



The Hutchinson-MacLennan " lime requirement " method 

 has given useful results in the hands of certain workers but not 

 of all. The variations in " lime requirement " resulting from 

 changes in the amounts of soil and calcium bicarbonate are shown 

 to be connected with buffer action of the soil, as determined by 

 electrometric measurements of the hydrogen ion concentration, 

 after the addition of lime water. A systematic difference between 

 the direct electrometric titration curves and the indirect titration 

 curves calculated from the calcium bicarbonate experiments, is 

 due to the variable calcium concentration of the bicarbonate 

 solutions. In the presence of calcium chloride both methods 

 show higher acidities for a given base absorption, and 

 give almost identical titration curves. The Hutchinson-Mac- 

 Lennan " lime requirement " is always less than that equivalent 

 to the amount of lime required to give a neutral solution 

 (pH = 7.0) in the electrometric titrations, a result which accords 

 with the field results quoted in the preceding papers. The calcium 

 bicarbonate solutions after treatment with soil are quite acid, 

 with pH values always less than 6.2, but the salt effect tends to 

 give higher base absorption than is given for the same pH value 

 in the titration Curves. Better values for the " lime require- 

 ment " are obtained by interpolating the results to a constant, 



